The present invention relates to a method and apparatus for establishing an anchor inside of a retaining wall to prevent a retaining wall surrounding a raised portion of ground or a retaining wall surrounding a vacant space formed below ground surface from tumbling down, that is, to increase the resistance against external forces exerted upon a retaining wall in the direction of causing the retaining wall to tumble down.
In the case of an anchor for increasing resistance against lateral pressure exerted upon a retaining wall on a side surface of a precipice, that is, upon a precipice retaining wall, that is established in an oblique direction with respect to the precipice retaining wall, the extreme end portion of said anchor must be supported by any means in the earth. However, since said support end portion is substantially distant from the outer surface of the precipice retaining wall, the work of establishing such a support is extremely difficult.
It is an object of the present invention to provide a novel method and apparatus for establishing an anchor which makes it possible to easily form an anchor having a bulb-shaped support portion having a very high withdrawal resistance within the ground remote from a retaining wall.
Another object of the invention is to provide a novel method and apparatus for reducing the rotational resistance incident to excavating an auger bore in the ground by means of an earth auger.
Still another object of the invention is to provide a method and means for facilitating the operation of disconnecting a rod from an anchor and withdrawing the same after the use of the anchor has ended.
Yet another object of the invention is to provide a method and means for facilitating the adjustment of the driving direction of an earth auger with respect to a retaining wall surface.
According to one feature of the present invention, a method and apparatus for establishing an anchor is characterized in that an auger bore is excavated through and inside of a retaining wall with an earth auger while expansible blades provided just above an auger head are contracted, thereafter the expansible blades are expanded by reversing the rotation of the earth auger to form an enlarged bore having a larger diameter at the extreme end portion of said auger bore by means of said expansible blades, an auger shaft is separated from the auger head and withdrawn out of the auger bore while leaving an anchor plate formed integrally with said auger head as well as a rod connected to said anchor plate within the enlarged bore and the auger bore, and then mortar is filled in said enlarged bore and said auger bore, whereby an anchor made of concrete and having a bulb-shaped enlarged portion at its extreme end may be established.